A Hierarchical Operation Strategy of Parallel Inverters for Efficiency Improvement and Voltage Stabilization in Microgrids

The well-known droop controlled parallel voltage source inverters are widely used in islanded microgrids to realize proportional power sharing based on ratings. However, when considering different loss characteristics of inverters, traditional droop control method is not an optimal power allocation scheme. This paper proposed a novel hierarchical operation strategy to realize overall efficiency optimization and voltage stabilization for parallel inverter system. Firstly, a tertiary efficiency optimization strategy is developed to reallocate power sharing among different inverters, minimizing total operation losses. Secondly, combined with droop characteristic, a master-slave control scheme is proposed to realize automatic voltage regulation and accurate output power adjustment on primary level. Furthermore, a secondary control method is implemented to restore system frequency and voltage after output power variation. Finally, comparison results based on simulation are presented to show the advantages of this proposed strategy over traditional methods.